DIRECT OBSERVATION BY SCANNING-TUNNELING-MICROSCOPY OF THE 2-DIMENSIONAL LATTICE STRUCTURE OF THE S-LAYER SHEATH OF THE ARCHAEOBACTERIUM METHANOSPIRILLUM-HUNGATEI GP1

Observation of the two-dimensional (2-D) 3 nm x 3 nn lattice structure of the S-layer sheath of the archaeobacterium Methanospirillum hungat ei is reported for the first time by scanning tunneling microscopy. Th e samples consisted of sheath fragments deposited on a TaSe2 substrate and coated with a Pt/Ir film. In addition to confirming the 2-D struc ture, the images reveal some new information about the nano-scale deta ils of the sheath structure. A lateral resolution of 1 nm was achieved , suggesting that the grain size of the Pt/Ir films was much less than for similar films deposited on a smooth metal surface.